The present invention relates to pumps, and more particularly, to positive-displacement rotary vane pumps.
Rotary vane pumps operate through the action of a number of rotating vanes or blades. A conventional rotary vane pump includes a rotor assembly eccentrically positioned within a pumping chamber. A number of vanes are spaced around the rotor to divide the pumping chamber into a series of cavities. As the rotor rotates, these cavities rotate around the pumping chamber continually changing in volume due to movement of the vanes and the eccentric alignment of the rotor and pumping chamber. An inlet communicates with the pumping chamber on the side of the pump where the cavities expand. Similarly, an outlet communicates with the pumping chamber on the side of the pump where the cavities contract. As each cavity expands, a partial vacuum is created to draw fluid into the pump through the inlet. As the cavity contracts, the pressure within the cavity increases forcing the fluid out of the pump through the outlet. The expansion and contraction process continues for each cavity to provide a continuous pumping action.
Most rotary vane pumps can be broadly classified in one of two categories--sliding vane and hinged vane. Sliding vane rotary pumps include generally straight vanes slidably fitted within radially extending slots formed in the rotor. As the rotor spins, centrifugal force and hydraulic pressure maintain the vanes in firm contact with the liner of the pumping chamber. However, shear force in the vane slot resists the sliding movement of the vanes. With relatively viscous pumpage, the shear force may cause the vanes to stick within the vane slots.
Hinged vane rotary pumps include vanes that are pivotally secured to the rotor (See FIG. 1 and U.S. Pat. No. 4,960,371, issued Oct. 2, 1990, to Bassett). The vanes 200 include an inner end 202 hinged to the rotor 204 and an outer end 206 in contact with the liner 208 of the pumping chamber. As the rotor 204 spins, the centrifugal force and hydraulic pressure of the pumpage urge the vanes 200 outward against the liner 208. Unlike sliding vanes, hinged vanes are not adversely affected by shear force. In fact, because the vanes are angled into the direction of rotation, shear force actually helps to push the vanes outward into firm contact with the liner.
Hinged vane rotary pumps also have a larger per revolution pumping capacity than conventional sliding vane pumps of the same housing and rotor dimensions. The pumping capacity of a rotary pump is dependant in part on the maximum volume of each pumping cavity. The volume of a pumping cavity in a sliding vane rotary pump is defined by the inner surface of the liner, the outer surface of the rotor, and the opposing surfaces of the bounding vanes. Hinged vane rotary pumps, on the other hand, include vane pockets that seat the vanes as they fold inward. When the vanes fold outward, these pockets are open to receive pumpage, thereby significantly increasing the capacity of the pump.
Hinged vanes are, however, relatively susceptible to wear. As the vanes rotate, the outer ends are in virtually continuous contact with the liner of the pumping chamber, causing both the vane tips and the liner to wear. Eventually, the liner and vanes must be replaced. Vane wear can also severely damage the pump. As the vanes wear, they pivot farther outward. The hydraulic pressure applied across the entire face of the vane acts to pivot the vane outward. Over time, the vanes can pivot outward far enough and/or under sufficient hydraulic force to bind against the liner, causing the pump to seize in a manner similar to a sprag clutch.